1. Field of the Invention
This invention relates to a multi-layer wiring board and a method of manufacturing the same.
2. Description of the Prior Art
In recent years, multi-layer wiring boards having stacked therein insulating bases in which wiring layers are formed are being frequently used as miniaturization of electronic devices proceeds. Known among such multi-layer wiring boards is a multi-layer wiring board that, in order to meet requirements of further miniaturization, and so on has a configuration combining a multi-layer wiring unit and a cable unit, the multi-layer wiring unit being a multi-layer wiring part with a multi-layer structure and having a wiring layer on which an electronic component is mounted exposed in a surface layer, and the cable unit being a cable part continuous from this multi-layer wiring unit and having flexibility (refer to, for example, Japanese Unexamined Patent Application Publication No. H7-58425 A).
However, in the multi-layer wiring board of conventional technology disclosed in the above-mentioned Japanese Unexamined Patent Application Publication No. H7-53425 A, an upper surface of the wiring layer of the cable unit is covered by a cover layer film that can be used as an adhesive layer of a rigid board. Therefore, the cover lay film includes a function as an adhesive agent, and there is a problem that handling during thermal compression bonding is difficult.
In addition, the multi-layer wiring unit and the cable unit are configured by materials of different characteristics, hence there is a risk that it is easy for stress to be generated causing variation in stretching properties or flexibility of the board, for distortion to occur at a boundary place of these portions, and furthermore for inter-layer peeling to occur due to a difference in coefficient of thermal expansion, and so on, whereby reliability falls.